1. Field of the Invention
The present invention relates to novel imidazole compounds and photosensitive members utilizing them. More particularly, it relates to novel 1,2,4,5-benzoylenebis (anthraquinone[1,2-d]imidazole) compounds, which are organic photoconductive substances, and photosensitive members for electrophotography having a photosensitive layer containing the novel compounds.
2. Description of the Prior Art
Generally, an electrophotography using a photoconductive photosensitive member is one of information recording means utilizing photoconductive phenomena.
In the electrophotography, the surface of the photosensitive member is uniformly charged by a corona discharge or the like, in darkness and then, by subjecting the charged surface to image exposure, the electric charge of the exposed portion is discharged selectively to form an electrostatic latent image at the unexposed portion of the surface. Next, the latent image is converted to a visual image by allowing charged colored fine particles (toner) to adhere to the latent image by means of electrostatic attraction force, etc., whereby an image is formed. The basic properties required for photoconductive photosensitive members used in the electrophotography technics of these serial processes are:
(1) that the photosensitive members can be electrified in darkness at a suitable electric potential uniformly,
(2) that they have a high, electric charge-retentivity in darkness and discharge of the electric charge from them is minor,
(3) that they are superior in photosensitivity and quickly discharge the electric charge by photoirradiation, and the like. Moreover, it is required for the photoconductive photosensitive members to have good stability and endurance; such as, that the surface of them can be discharged easily, with a minor residual electric potential on the surface, that they have mechanical strength and are superior in flexibility, that their electric properties, especially, electrification property, remaining electric potential, etc., do not fluctuate even when they are used repeatedly, that they are resistant to heat, light, temperature, humidity, ozone deterioration. etc., and the like.
Photosensitive members for electrophotography now used practically may be divided broadly into two groups, one utilizing materials of inorganic series and one utilizing materials of organic series.
As representative photosensitive members of inorganic series, there can be mentioned those of selenium series, such as amorphous selenium (a-Se), amorphous arsenic selenide (a-AS.sub.2 Se.sub.3), etc., those comprising color-sensitized zinc oxide (ZnO) or cadmium sulfide (CdS) dispersed in a bonding resin, those using amorphous silicon (a-Si), and the like. As representative photosensitive members of organic series, there are those using a charge-transfer complex of 2,4,7-trinitro-9-fluorenone (TNF) and poly-N-vinylcarbazole (PVK), and the like.
These photosensitive members have many merits, but at the same time some demerits. For instance, photosensitive members of selenium series and photosensitive members using CdS have some questions in respect of their heat-resistance and can-stability. Moreover, there is a restriction in the use of those photosensitive members that, because of their toxicity, they cannot be simply thrown away but have to be recovered. Photosensitive members comprising ZnO dispersed in resin are now practically not used, because of their low sensitivity and inferior endurance. Amorphous silicon photosensitive members having merits, such as high sensitivity, high endurance, etc., have also problems that their manufacturing cost is high because of their complicated manufacturing process, that they give faulty images resulting from the fault of membrane which is inherent in amorphous silicon, and the like. Further, they have defects that their flexibility is not a satisfactory one, that their processing into various forms such as drum, sheet, etc., is not easy, and the like.
On the other hand, attention is given to organic photosensitive members as the most important ones, because suitable organic materials without the problems on canstability and toxicity can be selected from existing various materials or organic materials having improved durability and low cost become available. However, there remains another disadvantage on sensitivity of organic photosensitive materials to be improved. The above described PVK-TNF charge-transfer complex series resulted from such improvement, but did not attain sufficient sensitivity. In addition, various sensitizing methods have been proposed. At present, the main current of organic photosensitive members practically used is occupied by laminate type photosensitive members (hereinafter, called "multilayer type photosensitive members") having a superior sensitizing property, which comprise a layer (hereinafter, called "charge-generating layer') containing a substance which allows generation of chargecarriers by photoirradiation (hereinafter, called "chargegenerating substance") and a layer (hereinafter, called "charge-transporting layer") consisting mainly of a substance which accepts and transports the charge carriers generating in the charge-generating layer (hereinafter, called "charge-transporting substance").
As organic materials which may be used for the chargegenerating layer of the above-mentioned multilayer type photosensitive members, bis-azo pigments such as chlorodianblue, etc., polycyclic quinone series pigments such as dibromoanthanthrone, etc., perillene, quinacridone or phthalocyanine series compounds, azulenium salt compounds, and the like, are known. However, some of these chargegenerating materials are lacking in photoconductivity though they have a good absorption spectral property for photosensitive members, in the visual ray region, and some of them have an absorption spectral property not suitable for photosensitive members though they have a good photoconductivity. Thus, it was very difficult to compose a photosensitive members having a good sensitivity, by striving for coexistence of the absorption spectral property and the photoconductivity. The multilayer type photosensitive members provided with such charge-generating layer which have been hitherto proposed are, for example,
1. those wherein a thin layer formed by application of an organic amine solution of chlorodianblue is used as the charge-generating layer and a hydrazone compound is used as the charge-transporting substance of the charge-transporting layer (Japanese Patent Publication No. SHO 55-42380 is referred to),
2. those wherein a bis-azo compound is used as the charge-generating substance of the charge-generating layer and a hydrazone compound is used as the charge-transporting layer (Japanese Patent Application Laid-open No. SHO 59-214035 is referred to),
3. those wherein an azulenium salt compound is used as the charge-generating substance of the charge-generating layer and a hydrazone compound or the like is used as the charge-transporting layer (Japanese Patent Application Laid-open No. SHO 59-53850 is referred to),
4. those wherein a perillene derivative is used as the charge-generating substance of the charge-generating layer and an oxadiazole derivative is used as the charge-transporting layer (U.S. Pat. No. 3,871,882 is referred to), and the like.
However, these photosensitive members 1.-4. were still insufficient in sensitivity, as they were used practically. Moreover, these hitherto known multilayer type photosensitive members had a problem in their stability as they were used repeatedly.
Therefore, notwithstanding the above-mentioned many merits of the organic photoconductive substances, compared with inorganic ones, they were not so much used for photosensitive members for electrophotography because photosensitive members using them were inferior in sensitivity and endurance.
The present invention has been made in view of the above-described circumstances and its purpose resides in providing organic photosensitive members for electrophotography having a high sensitivity and a superior stability on repeated use.
As a result of keen investigations for organic photoconductive substances having a high sensitivity and a high endurance, which have been performed from the above-described view-points, the inventors of the present invention have found that a specific group of novel imidazole compounds which were not yet disclosed in the literature are suitable as the organic photoconductive substances. Thus, the present invention has been completed.